1. Field of the Present Invention
The present invention relates to a technology for correcting distortion of servo information generated using a common master medium.
2. Description of the Related Art
Conventionally, there has been a demand for an increase in the storage capacities of disk apparatuses like magnetic disk apparatuses. To increase the storage capacity of a magnetic disk apparatus, it is necessary to make the track pitch of a magnetic disk small and to write servo information at correct positions accurately. One of the methods that are used to write servo information at correct positions accurately is to give individual magnetic disk apparatuses a function to write the servo information at the correct positions accurately; however, this method makes the price of each magnetic disk apparatus high.
For this reason, another method in which after servo information is written onto a magnetic disk, the magnetic disk having the servo tracks written is installed in each apparatus has been considered. In such a magnetic disk apparatus, it is extremely important to determine the position of the head accurately on the target track for improvement of the recording density of the magnetic disk. The information used to control the determination of the position with respect to the target track is recorded on the magnetic disk medium and is called servo signals. The processing of recording the servo signals for the magnetic recording apparatus is called “servo track write (STW)”. Various methods of STW have been proposed.
An example of STW method is to form servo information, using a common master medium for magnetic transfer, discrete track, and patterned media, and the like. When this method is used, the servo information is generated on each of the magnetic disks by manufacturing a large number of duplicated magnetic disks from the mold in common. In this situation, a problem arises where a distortion in the mold makes the determination of the position with respect to the target track inaccurate. Thus, it is necessary to determine the position with respect to the target track, after the deviation of the track position due to a distortion in the mold or the like is corrected.
Methods for controlling the determination of the position of the head by correcting the deviation in the position of the track due to a distortion in the mold or the like includes a method in which the deviation in the position of the track is followed and another method in which a virtual track is generated so that the deviation in the position of the track is not followed, but the virtual track is followed. Various proposals have been made as to which one of these methods should be used.
For example, Japanese Patent Application Laid-open No. 2004-342316 discloses a magnetic disk with which a control unit that controls the determination of the position according to a position error of the magnetic head based on the servo information performs a feed-forward control on the position determination process by following the measured rotation frequency component of the magnetic disk and eliminating a high-order frequency component that has a higher frequency than the rotation frequency.
With the above technology, to correct distortion information on the disk (the servo information) caused by the mold or the like, the rotation frequency component of the magnetic disk and the high-order frequency component that has a higher frequency than the rotation frequency are measured for each magnetic disk apparatus. Thus, a problem arises where it takes a long period of time to correct the distortion information for the magnetic disk apparatus. Because of the problem, it takes a long period of time to manufacture each magnetic disk apparatus, and the level of productivity is lowered. The higher the recording density of each magnetic disk apparatus becomes, the bigger the influence of these problems is.